Most conventional submerged arc furnaces include a plurality of electrode columns, generally three, which each include an electrode and an electrode column mantel in which the electrode is concentrically located and is vertically slidable. The mantels are themselves slidable through suitable seal arrangements in the roof of the furnace.
The electrode mantels each include hanger arrangements from which a pressure ring and the electrical contact shoe assemblies for the electrode are suspended to be located around the electrode a little above the material in the furnace. The electrode column mantels are complicated arrangements which are connected to electrical and cooling water services by flexible cooling water supply hoses and electrical bus-tube connections.
The majority of electrodes used in furnaces of the above type are those known as Söderberg electrodes which consist of an electrode casing which extends from the top of the electrode to below the electrode contact shoes in the furnace and an electrode portion which initially consists of a carbon based paste in the electrode casing which is baked by furnace heat into an electrically conductive solid cylindrical form in the lower portion of the electrode casing. The lower end of the casing is burned from the solid portion of the electrode, from below the contact shoes, by furnace heat. A large portion of the exposed length of the solid portion of the electrode is located in the furnace material in use. The electrode column is supported in the furnace by electrical load regulating rams which act between an electrode clamp slipping arrangement and a suspended floor in the furnace building above the furnace roof.
The electrode clamp slipping arrangement generally consists of upper and lower slipping clamps which are sequentially operated and moved to extend the electrode as the tip of the electrode is consumed in use in the furnace material.
A major problem with furnaces of the above type is that of electrode breakage. An electrode break at or towards its end in the furnace material due, to perhaps uneven baking of the paste due to inconsistent furnace conditions, such as furnace material movement and so on which could induce stresses in the baked region of the electrode which ultimately lead to the electrode break. The breaks are unpredictable and difficult to detect once broken. It not infrequently happens that the electrode break is not detected by the furnace operator until a fire or in the worst case, an explosion, occurs in the furnace seriously compromising the safety of personnel in the vicinity of the furnace and the integrity of the furnace itself.
In order to minimise serious furnace downtime and the problems mentioned above due to electrode breakage, systems have been developed for detecting the breakage of an electrode in the furnace in use. In all of the known electrode break detection arrangements load cells or the like which are acted on by the electrode electrical load regulating cylinders are employed continuously to monitor the mass of the entire electrode columns and so indirectly the mass of the electrodes, in use. This electrode mass measuring arrangement is, however, highly complicated by forces acting on the total electrode column. These forces include, amongst others, the electrode contact shoe pressure on the electrode, the load variations on the mantel by roof seal friction, the mass of water and even direct load forces applied to the exposed tip portions of the electrodes by furnace rabbling and sludge with all of these parameters, some of which are unpredictable, having to be taken into calculation account in arriving at the electrode mass.